Conventionally, a hydraulic cylinder is used for mold clamping in a press machine or the like. For efficient production, the mold clamping is usually performed by moving a die at high speed until the die abuts a work and then pressing the die against the work with high power. A hydraulic cylinder that is used for such a press machine needs a relatively small power for moving the die but needs a high power for pressing the die. Therefore, different hydraulic cylinders may be disposed individually for moving the die and for pressing the die. Alternatively, a ram having a small area for receiving a pressure for moving the die may be embedded in a rod so that the die can be moved at high speed.
In either case, it is necessary to supply hydraulic oil directly from a tank for compensating increase of capacity of cylinder chamber for pressing when moving the die at high speed, while it is necessary to prevent the hydraulic oil for pressing from leaking into the tank when pressing the die. In addition, it is necessary to permit a large quantity of oil in the cylinder chamber for pressing to be discharged into the tank when returning the die from a clamping position to a waiting position.
In order to satisfy these requirements, if different hydraulic cylinders are disposed for moving the die and for pressing the die individually, there is proposed a hydraulic cylinder device 8 utilizing a profile valve 81 that can obtain a large quantity of flow with little pressure drop as shown in FIG. 10, for example (non-patent document 1).
Furthermore, the applicant has proposed and disclosed a fluid pressure cylinder device that can perform both high speed drive and high power drive by one fluid pressure cylinder (patent document 1).
This fluid pressure cylinder device includes a fluid pressure cylinder, a reciprocating pump having two supply and discharge ports for supplying and discharging hydraulic fluid for driving the fluid pressure cylinder in a reciprocating manner and a motor for rotating the reciprocating pump selectively in a forward or a backward direction. The fluid pressure cylinder includes a cylinder tube, a piston that slides inside the cylinder tube, covers for closing both end faces of the cylinder tube and a rod that is connected to the piston and pass through one of the covers. A forward side cylinder chamber of the fluid pressure cylinder is divided into a high speed cylinder chamber having the same effective area for receiving pressure as a backward side cylinder chamber that is a cylinder chamber on a backward side and a high power cylinder chamber having a remaining effective area for receiving pressure. Furthermore, there is provided a valve for switching so that the hydraulic fluid supplied from the reciprocating pump is selectively supplied to the high power cylinder chamber.
[Non-patent document 1] http://www.yuken.co.jp/japanese/pdf/E407.pdf
[Patent document 1] Japanese unexamined patent publication No. 2002-147404